You can't explore the hallways of Gekkoukan High in Persona 3: Portable. Sorry. When Atlus scaled down Shin Megami Tensei Persona 3 for the PSP they had to make some changes.
As seen in this movie, story sequences are told visual novel style with blinking character portraits on static backgrounds. The 3D models from the PlayStation 2 game are out of the picture. When it's time to explore the world, players point and click to interact with people and enter places.